Gas Pool Heater Running but not Heating? Here’s What To Do

When the outdoor temperature gets colder, you might find that gas pool heaters are a great way to keep your pool water warm. But if you have a malfunctioning gas pool heater, then your pool water will get chilled rather quickly in the fall or spring seasons.

This doesn’t mean you need to call a professional, though. There are ways to troubleshoot the heater in order to see where the problem lies. Let’s explore all the common problems that can happen with a gas pool heater and the best ways to fix them.

Common Problems with Gas Pool Heaters

To understand gas pool heater troubleshooting better, we must examine the most common issues which cause it to malfunction. Then you can learn how to resolve the problem without professional assistance.

Heater Ignition Failure

The most common issue with gas pool heaters is that they don’t ignite. This can happen every now and then for several different reasons. First, see if the heater switch is activated. Next, check the thermostat temperature and make sure it is set higher than the temperature of the water. After that, see if the pilot is still lit or not. Also, the gas supply valve should be in its “on” position.

Pilot Does Not Light

There are a few reasons why your pilot may not light. Your heater may have low gas pressure, poor venting, or weak air supply. Inspect each vent to ensure nothing is interfering with the heater. Also, make sure you have normal pressure, and the gas is turned on.

Water Temperature Doesn’t Match the Set Temperature

You might have a low setting on the thermostat if this is happening. Perhaps you have a very small heater for a pool of your size. If enough gas is not going to your heater, that could be a problem too. Check to see if you have a faulty high limit switch because it might be causing the heater to deactivate before the water gets heated properly. Sometimes your heater may be running when the outdoor temperature is too cold. If that happens, wait for the temperature outside to warm up.

On and Off Cycling of the Heater

The water must be heated to the set temperature before the heater cycles to the off position. But if the cycling between on and off takes place before the desired water temperature is reached, then the water flow might be the problem. Check to see if you have a clogged filter, reversed water connections, or a closed valve. In other cases, you may have a bad thermostat which must be replaced.

Leaky Heater

Your pool water has all kinds of sanitizing chemicals in it. However, the heat exchanger will eventually get damaged from the constant exposure to these chemicals. This could cause your heater to leak. The cold winter temperatures can cause this to happen too. You could replace the heat exchanger if you’re confident that’s the problem. But first, make sure you don’t have a loose connection or leaky gasket. If they appear to be fine, then you can pursue the more expensive options for fixing the problem.

Leaky Heater While Burner is Lit

If it is extremely cold outside and the burner is lit, then condensation can accumulate and drip from the heater. Sometimes the leak may be from too much water flow or a damaged internal bypass. Consider an external pool water heater bypass installation to lower the flow of water that goes to the heater.

Dark Exhaust

If too much heat is damaging your heater, then you might see dark exhaust coming out of it when it’s on. In this situation, monitor your gas pressure and see if you have enough air available and good venting. Sometimes wind or a downdraft may be responsible for this problem. A high wind stack installation may be needed to fix the issue.

Heater Rust

The sanitizing chemicals in the water can damage more than just your exhaust. They can also corrode the pool heater too. You’ll notice this is happening if you see rust anywhere in the pool as your heater is turned on. If you own a cast iron heater, then this problem is very common. Test the water of your pool and see if the chemicals are balanced. Replacing corroded components may be required if nothing else works.

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